In “This Is the End,” Michael Cera’s unbridled, drug-fueled narcissism was a punchline—the shockingly raunchy and outgoing behavior of an actor perceived to have as much edge and in-your-face personality as non-fat fro-yo. (With all due respect, Forever Yogurt.)

In the unexpectedly powerful “Crystal Fairy,” Jamie’s (Cera) narcissism is far less amusing. Hanging in Chile with little on his mind than a variety of illegal intoxicants, Jamie’s so selfishly and restlessly driven toward his idea of fun that he detracts from everyone else’s. Powered at a party by a little weed and a lot of coke, Jamie invites a girl who calls herself Crystal Fairy (Gaby Hoffman of “Sleepless in Seattle”!) to join Jamie, his roommate Champa (Juan Andres Silva) and Champa’s two brothers on a trip to secure the legendary San Pedro cactus and ingest its majesty on a remote beach. The next day Jamie resents Crystal taking his invitation as an invitation and wants to ditch her, but Champa’s good people. He says that Crystal’s now part of their group and, unlike his increasingly aggressive American pal, doesn’t judge Crystal’s abundant body hair or unrestrained sense of self.

I wouldn’t blame you if you thought this adventure turned into a live-action version of Homer Simpson’s mind-altering hot pepper journey. Written and directed by Sebastian Silva (who also directed Cera in the upcoming “Magic Magic”), “Crystal Fairy” in fact dares to focus on a largely objectionable main character and show the group dynamic shifts less from the addition of a free-spirited stranger than from Jamie’s reaction to her. She is loopy, but Silva doesn’t make her out to be perfect, and Hoffmann’s performance makes Crystal a believable person instead of a contrived, only-in-the-movies weirdo.

At times, this is a strange and somewhat repetitive movie. Yet Silva, who was wise to cast his family members, maintains masterful command of a story that’s sometimes funny and ultimately devastating. It’s the rare achievement that can ask both “How much are we all driven by our fears?” and “What does a scrawny, arrogant American look like doing late-night, drug-induced stretching in his underwear?”

When Jamie first meets Crystal, she’s dancing up a storm and he tells her, “You’re embarrassing yourself.” “We’re all one self, man!” she responds, seemingly unfazed. In “Crystal Fairy,” an emotional as much as a physical journey, Crystal’s statement proves true in that we often only know ourselves through interactions with others. And don’t always like what we see.

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